So I want to get the flux dmcc light but its looking like I wont have the money for them so these are my other choices. I just want a good all around all mountain binding to go with my rome reverb rocker and thirty two binary boa boots. The reason I am only looking at flux is because that is all my local boardshop carries other than burton for bindings.

DMCC light has a stiffer base than TT30 due to carbon infusion. DMCC light highback is softer by design but has same material composition as TT30.

The following comment is my interpretation:
TT30 and DS30 base have the same composition but the TT30 will be stiffer by design due to Alpha base (allows more ankle roll). Note, Alpha base has inserts to stiffen flex if desired.

DMCC light has a stiffer base than TT30 due to carbon infusion. DMCC light highback is softer by design but has same material composition as TT30.

The following comment is my interpretation:
TT30 and DS30 base have the same composition but the TT30 will be stiffer by design due to Alpha base (allows more ankle roll). Note, Alpha base has inserts to stiffen flex if desired.

How would a stiffer highback soft baseplate differ from the softer highback, stiffer baseplate (I have an idea, but I'm interested in the design reasoning).

The flex progression I posted (via Lady Flintstone) was for the binding as a whole.

Based on the design of the highback, your highback flex progression should be changed to SF45 > TT30 > DMCC Light & DS30. Because the DMCC Light and DS30 have the same highback. Unless you opt for the DS30 Limited highback.

BTW, I'm not a rep and haven't tried either binding side by side, but I think Nivek has compared them.

As for your last question, I have no idea. But my guess is the DS30 Limited would be stiffer than the standard issue DS30.